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This patch introduces two additional lock modes for tuples: "SELECT FOR KEY SHARE" and "SELECT FOR NO KEY UPDATE". These don't block each other, in contrast with already existing "SELECT FOR SHARE" and "SELECT FOR UPDATE". UPDATE commands that do not modify the values stored in the columns that are part of the key of the tuple now grab a SELECT FOR NO KEY UPDATE lock on the tuple, allowing them to proceed concurrently with tuple locks of the FOR KEY SHARE variety. Foreign key triggers now use FOR KEY SHARE instead of FOR SHARE; this means the concurrency improvement applies to them, which is the whole point of this patch. The added tuple lock semantics require some rejiggering of the multixact module, so that the locking level that each transaction is holding can be stored alongside its Xid. Also, multixacts now need to persist across server restarts and crashes, because they can now represent not only tuple locks, but also tuple updates. This means we need more careful tracking of lifetime of pg_multixact SLRU files; since they now persist longer, we require more infrastructure to figure out when they can be removed. pg_upgrade also needs to be careful to copy pg_multixact files over from the old server to the new, or at least part of multixact.c state, depending on the versions of the old and new servers. Tuple time qualification rules (HeapTupleSatisfies routines) need to be careful not to consider tuples with the "is multi" infomask bit set as being only locked; they might need to look up MultiXact values (i.e. possibly do pg_multixact I/O) to find out the Xid that updated a tuple, whereas they previously were assured to only use information readily available from the tuple header. This is considered acceptable, because the extra I/O would involve cases that would previously cause some commands to block waiting for concurrent transactions to finish. Another important change is the fact that locking tuples that have previously been updated causes the future versions to be marked as locked, too; this is essential for correctness of foreign key checks. This causes additional WAL-logging, also (there was previously a single WAL record for a locked tuple; now there are as many as updated copies of the tuple there exist.) With all this in place, contention related to tuples being checked by foreign key rules should be much reduced. As a bonus, the old behavior that a subtransaction grabbing a stronger tuple lock than the parent (sub)transaction held on a given tuple and later aborting caused the weaker lock to be lost, has been fixed. Many new spec files were added for isolation tester framework, to ensure overall behavior is sane. There's probably room for several more tests. There were several reviewers of this patch; in particular, Noah Misch and Andres Freund spent considerable time in it. Original idea for the patch came from Simon Riggs, after a problem report by Joel Jacobson. Most code is from me, with contributions from Marti Raudsepp, Alexander Shulgin, Noah Misch and Andres Freund. This patch was discussed in several pgsql-hackers threads; the most important start at the following message-ids: AANLkTimo9XVcEzfiBR-ut3KVNDkjm2Vxh+t8kAmWjPuv@mail.gmail.com 1290721684-sup-3951@alvh.no-ip.org 1294953201-sup-2099@alvh.no-ip.org 1320343602-sup-2290@alvh.no-ip.org 1339690386-sup-8927@alvh.no-ip.org 4FE5FF020200002500048A3D@gw.wicourts.gov 4FEAB90A0200002500048B7D@gw.wicourts.gov
82 lines
2.7 KiB
C
82 lines
2.7 KiB
C
/*-------------------------------------------------------------------------
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*
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* pg_database.h
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* definition of the system "database" relation (pg_database)
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* along with the relation's initial contents.
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*
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*
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* Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* src/include/catalog/pg_database.h
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*
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* NOTES
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* the genbki.pl script reads this file and generates .bki
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* information from the DATA() statements.
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef PG_DATABASE_H
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#define PG_DATABASE_H
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#include "catalog/genbki.h"
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/* ----------------
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* pg_database definition. cpp turns this into
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* typedef struct FormData_pg_database
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* ----------------
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*/
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#define DatabaseRelationId 1262
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#define DatabaseRelation_Rowtype_Id 1248
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CATALOG(pg_database,1262) BKI_SHARED_RELATION BKI_ROWTYPE_OID(1248) BKI_SCHEMA_MACRO
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{
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NameData datname; /* database name */
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Oid datdba; /* owner of database */
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int32 encoding; /* character encoding */
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NameData datcollate; /* LC_COLLATE setting */
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NameData datctype; /* LC_CTYPE setting */
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bool datistemplate; /* allowed as CREATE DATABASE template? */
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bool datallowconn; /* new connections allowed? */
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int32 datconnlimit; /* max connections allowed (-1=no limit) */
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Oid datlastsysoid; /* highest OID to consider a system OID */
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TransactionId datfrozenxid; /* all Xids < this are frozen in this DB */
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TransactionId datminmxid; /* all multixacts in the DB are >= this */
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Oid dattablespace; /* default table space for this DB */
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#ifdef CATALOG_VARLEN /* variable-length fields start here */
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aclitem datacl[1]; /* access permissions */
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#endif
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} FormData_pg_database;
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/* ----------------
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* Form_pg_database corresponds to a pointer to a tuple with
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* the format of pg_database relation.
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* ----------------
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*/
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typedef FormData_pg_database *Form_pg_database;
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/* ----------------
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* compiler constants for pg_database
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* ----------------
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*/
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#define Natts_pg_database 13
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#define Anum_pg_database_datname 1
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#define Anum_pg_database_datdba 2
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#define Anum_pg_database_encoding 3
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#define Anum_pg_database_datcollate 4
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#define Anum_pg_database_datctype 5
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#define Anum_pg_database_datistemplate 6
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#define Anum_pg_database_datallowconn 7
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#define Anum_pg_database_datconnlimit 8
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#define Anum_pg_database_datlastsysoid 9
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#define Anum_pg_database_datfrozenxid 10
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#define Anum_pg_database_datminmxid 11
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#define Anum_pg_database_dattablespace 12
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#define Anum_pg_database_datacl 13
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DATA(insert OID = 1 ( template1 PGUID ENCODING "LC_COLLATE" "LC_CTYPE" t t -1 0 0 1 1663 _null_));
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SHDESCR("default template for new databases");
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#define TemplateDbOid 1
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#endif /* PG_DATABASE_H */
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